Generally, in order to form an integrated circuit or a logic device, a process for forming a desired thin film on a surface of a semiconductor wafer, an LCD substrate or the like, or a process for etching such thin film in a desired pattern is repeatedly carried out.
For example, in a film forming process performed by a film forming apparatus, a thin film of silicon, a thin film of a silicon oxide or a silicon nitride, a thin film of a metal, a thin film of a metal oxide or a metal nitride, or the like is formed on a surface of a target object to be processed by having a predetermined processing gas (raw material gas) to react in a processing chamber. This thin film is deposited on the surface of the target object and is also adhered as an unnecessary adhesion film on surfaces of components in the processing chamber.
For example, FIG. 16 is a schematic diagram showing a part of a conventional mounting table structure provided in a film forming apparatus. A mounting table 2 made of, e.g., ceramic, is supported by a support 4 standing upright on a bottom portion of a chamber. A heater 6 is provided in the mounting table 2 to heat a semiconductor wafer W mounted thereon. Further, a ring-shaped cover ring 8 is provided around the periphery of the top surface of the mounting table 2 in order to prevent film formation on an end surface of the semiconductor wafer W. During the film formation, a temperature of the semiconductor wafer W is increased and, also, a temperature of a part of the side surface or the bottom surface of the mounting table 2 or the cover ring 8 as an in-chamber component is increased. Therefore, an unnecessary adhesion film 10 is deposited thereon. As the film formation reaction proceeds, residual reaction by-products are generated and exhausted together with an exhaust gas, and the unreacted processing gas remained therein without having reaction is also exhausted.
If the unreacted processing gas and/or the reaction by-product in the exhaust gas are directly discharged to the atmosphere, it causes environmental pollution or the like. Generally, in order to collect and remove the unreacted processing gas and/or the reaction by-product contained in the exhaust gas, a trap mechanism is installed at a gas exhaust system extending from a processing chamber. The unnecessary adhesion films adhered on the above-described components are removed and discarded by performing at regular intervals, e.g., wet cleaning in a state where the components are separated from the processing chamber or dry cleaning using a chloride- or a fluorine-based etching gas.
Various structures have been proposed for the trap mechanism in accordance with characteristics of a reaction by-product or the like to be collected and removed. For example, when a reaction by-product that is condensed (liquefaction) and solidified at a room temperature needs to be removed, the trap mechanism has a configuration in which a plurality of fins is provided in a housing having an inlet port and an outlet port of an exhaust gas. In this case, the fins are sequentially arranged along a direction in which the exhaust gas flows, so that the reaction by-product or the like in the exhaust gas is adhered to the surfaces of the fins and collected while the exhaust gas is passing through the fins. The collection efficiency can be increased by cooling the fins by a coolant or the like (see, e.g., Japanese Patent Application Publication No. 2001-214272).
Recently, in order to reduce wiring resistance or contact resistance, a thin film is formed by a film forming apparatus by using a raw material (source gas) of an organic metal compound containing a noble metal such as silver, gold, ruthenium or the like. In this case, there is proposed a recovery method for recovering a by-product containing an unreacted raw material by cooling and condensing an exhaust gas and for obtaining the unreacted raw material by purifying the by-product (see, e.g., Japanese Patent Application Publication No. 2001-342566).
However, in the above conventional film forming apparatus, dry cleaning using a chloride- or a fluorine-based etching gas is performed at regular intervals or irregular intervals. Thus, the unreacted raw material gas collected in the gas exhaust system during the film formation may be exposed to the etching gas to thereby be deteriorated. Accordingly, time and cost are required to perform the purifying process for recovering the raw material, or the collected raw material needs to be discharged from the gas exhaust system before the dry cleaning, which is complicated. Although a bypass line for bypassing the trap mechanism may be provided, the equipment becomes complicated.
In addition, since a thin film is deposited unnecessarily on the surfaces of the components in the processing chamber other than the semiconductor wafer as described above, the raw material gas is wasted, thereby decreasing the yield of the raw material. Especially, recently, a high-cost metal such as Ru (ruthenium) or the like is used as a film forming material, so that a method for effectively recovering a raw material or a metal contained in the raw material at a low cost is required.